Cavity resonator high-frequency apparatus



Nov. 23, 1954 L. P. SMITH CAVITY RESONATOR HIGH-FREQUENCY APPARATUS 3 Sheets-Sheet l Original Filed Nov. 16, 1944 INVENTOR. [m5/ .5m/m BY A l @fwfwy Nov. 23, 1954 L P, SMH-H 2,695,373

CAVITY RESONATOR HIGH-F`REQUENCY APPARATUS Original Filed Nov. 16, 1944 3 Sheeis-Sheet 2 -I -2 -s -4 -s -s -7 -s 7 1 INVENTOR. fly, 4. BYZMyH/W/r/f Nov. 23, 1954 L. P. SMITH 2,695,373

cAvITY RESONATOR HIGH-FREQUENCY APPARATUS original Filed Nov. 1e, 1944 3 sheds-sheet s 1 1 x 1 l l l l l,

IN V EN TOR.

-B Y l wwwa #Trae/viv United States Patent i CAVITY RESONATOR HIGH-FREQUENCY APPARATUS ration of America,a corporation of Delaware Continuation ofapplication. Serial No.'563,732, November 16, 1944. This application`-May '2, 1952, Serial No.f285,627

-35 Claims. (Cl. 315-5) vThis application is acontinuationof my copending application Serial No.563,732, filed November 16, 1944, .xassignedto the same assignee; now. abandoned `My inveritionl relates to generators of high frequency iradio -waves using cavity' resonatorsfand more particularly to electron. discharge devicesvsuch-as magnetrons utilizing cavity resonators and to ra method andV means for varying Vthe-k generated.; frequency.

IthasI become `necessaryto bezahle to Varythe' generr`ated frequency over a limited frequency range Vof a magne- .tronzorl other ultra high frequency generator using cavity f resonators as tank` circuits. A:quency change occur as-a kprescribed function of the time and with greater rapidity than'is practicalby-mechan- It-vis desirable to have the fre- Iical tuning ofthe-resonator. lt is further desirable that the power output shouldbe constant over the variable frequency* ra-nge.

lt is, therefore, yan objectof myr'invention to'provide a high-frequency? generator utilizing a cavity resonator vand -ameans for-varying orV modulating theV generated frevquency.

Another objectiefl my inventionfis Vto, provide an elec- `tronicy device Vusing-a Acavityresonator andfwhich can be utilized as a variable reactance Vdevice when coupled to a high frequency system.

-Astill'furtherobjectof my invention is to provide an electron discharge .device "utilizing cavityresonators which can be'frequency modulated.

kMore specifically -it vis-an object of my invention to prol'vide'a magnetron utilizing oneV or'more cavity resonators yand -whi`ch can be frequency modulated by electronic The novel features'whichifl believe` to be characteristic `of thy-invention are-set forth-with particularity in the -appended claims, but the-'invention itself will be best understood by reference tothefollowing description taken in connectionwith the accompanying drawing in which YFigures 2, '3 and 4 -are diagramsl which 4help toexplain the :principles of my invention, Figurel ist a vperspective view `with-parts broken 'away of 'oneembodiment 'of my invention, Figures -5 and. 6 are equivalentcircuits `showing operation ofapparatus'rnade` according to my invention,

Hbestbe `understood-"by reference to Figure l -which utilizes a cavity resonator,.the resonant frequency of vwhich be changed by electronic means.

In the` deviceV shown lprovide an-evacuatedenvelope la containinga rectangular cavity resonator 11 having di- `mensioiis "X, Y'and Z. The cavity' resonator is provided with oppositeiy disposed apertures 12 arid'13 in opposite walls thereof .throughwhich an electron beam is directed. T he eiectron beam is provided by means of the indirectly 'i heated cathode'll and can be controlledby thev grid 15.

rThe electroderlt on thelopposite side ofthe resonator. and

. in the path of the electron` beam .may be used in place of or in combination with the grid`f15. Transfer ofenergy to and from 'the cavity resonatortll may be had by .means of `thecoaxial-line 17 coupled. -to the resonator 11 bya `loop -117 coupled-to the-interior of the resonator.

Ai constant rice 32 magnetic lfield H is established along the path of the beam of electrons by means of a magnet having polepieces 18 j.and 19. A control inputcircuit includesthe transformer 20 and the voltage sources include the grid biasing voltage whethertheelectrode is to Vbe used as a collector or re- `flector.

\ Alternative larrangements for controlling the beam include the'circuit having' the transformery 25 for applying varying accelerating voltages to resonator 11 and vthe circuit including 'the transformer 25 connected to the electrode 16 for varying the voltage applied to this electrode when used as acontrol-electrode to reflect electrons back into the resonator.

ln order toset up an alternating electric eld within the resonator. someform of driving means is necessary. 1n the arrangementfshown a cavity resonator magnetron generator 26 whose frequency is to` be controlled is used as the driver. The magnetron 26 is provided with a cathode 27 and radially directed'in-like elements 28, the inner edges of which provide `the'anode segments. The wall of the envelope of the magnetron, which is a metallic envelope, and the tins orfslats'28 form the cavity resonators between adjacent anode segments. This form of magnetron is well-known. A magnetic eld is provided parallel tothe cathode in the space between the cathode and the anode segments. The coaxial line 17 has a couplingV loop 29 coupled to one of the magnetron resonators between adjacent anode segments. The coupling loop 17 of coaxial line' 17 is oriented Within the resonator 11 in a plane perpendicular to the beam path therein, so that a high frequency electricfieldE inthe Vdirection indicated is established therein.

The resonator 11 serves as a magnetron pilot cavity resonator'for varying lthe resonant frequency of the magnetron 26 to which it is coupled.

kThe constant magnetic iieldalong the Z direction of the resonator'll serves two purposes. 'It keeps the electron beam together and it is by'nieansof this magnetic field that electrons are made to movey in such away as to produce a large reactive current in the interior of the cavity resonator. The cavity resonator is assumed to be excited at an angular frequency w, with no electronbeam present, for eX- arnple, by the magnetron'26, although it could be excited by other means. This frequency corresponds to the normal mode of oscillation for whichthe electric field is always parallel to `the'X"direction of the resonator, that is,

transverse' to the directionofthey electron beam. When an 'electron moves in aiuniform transverse magnetic field H it will 'follow al circular path: The time T required to traverse a complete cycle'orcircle is where 1r is 3.1416, misthe massof Van .electron e is its charge and H is the magnetic'field intensity. Hence, this period of rotation is independent of both the linear velocity of the electron andthe radius of its circular path. The angular frequency of rotation of the electron is then When-an electron beam is made to traverse the cavity resonator 11V the resonant angular frequency of the reso- -nator in the particulary mode of oscillation under consideration changes-fromfw tow-l-Aanwhere. Aw depends upon the beam current, the transit angle `of the electrons through the resonatonand the magnetic field strength. The magnitude of the frequency-shift Aw may be readily computed wo is the electron rotation frequency dened above and where u is the transit angle in radians. The relationship (1 /dagli may also be written T(w-wo)-4, where 'r is the electron transit time through the resonator, since a equals m. The value of vis determined by the particular beam accelerating voltage and the dimension Z of the cavity resonator. Substituting for tw and wo the relationship becomes Where f is the operating frequency. When the magnetic field is adjusted for maximum frequency shift, the Aw is proportional to the square of the transit angle a. For values of magnetic field considerably different from that necessary to produce maximum shift, Aw can be shown to he proportional to a.

A better understanding of my invention may be had of the above by referring to Figures 2, 3, 4, and 6. Consider a pair of parallel plates P across which an alternating potential difference is applied resulting in an electric field of amplitude E and angular frequency w between the condenser plates, as shown in Figure 4. The uniform magnetic field is in the direction shown. An electron is projected into the field between the plates along the dotted line ab, parallel to the magnetic field. its linear velocity in this direction will remain constant so that at time t:0 the electron will be at position 1 and at time Az seconds later it will be at position 2, etc. At position l the electron has no velocity in the direction of E but on encountering the electric field E between positions l and 2, it will be accelerated in this direction. If the angular frequency .w of the oscillating electric field E were equal to the electron rotation frequency wo, each electron would remain in phase with the electric field and would be continuously accelerated so that it would receive more and more energy from the oscillating field and its motion would be a spiral of ever increasing radius. This condition would produce an electron current in phase with E at Vall positions, l, 2, and would constitute a loading or resistive component of current. If the condenser plates were to form a part of a resonant circuit, by connecting an inductance between the plates this resistive or in phase component would have no effect on the frequency but would reduce the Q of the circuit.

The transit time of the electron through the condenser plates from a to b and the relative values of w and wo can be chosen so that the net electron current is not in the direction of E but is in quadrature to E so that it constitutes a purely reactive current. To see how this comes about, let wn be somewhat less than iw. In this circumstance the electron Will not complete one revolution during one complete cycle of the oscillating field. Consequently it will lag behind E by a certain phase angle nqb so that as the time goes on the electron lags more and more behind E. It'will, however, continue to be accelerated until it lags behind E by 90 degrees. The electron then still increases its lagging phase angle by Ap on each revolution but the electron now is retarded by the oscillating field and'loses energy. It is evident that for a given value of o o, the time of flight of the electron between the condenser plates can be adjusted so that the energy acquired from the field in the period during which acceleration took place is iust given back to the field during the period of retardation and the net energy transfer from field to electron is zero. This situation is illustrated in Figures 2, 3 and 4. When an electron enters the plates at position l, Figure 4, it has no displacement from the median plane between the plates. This zero displacement is shown in Figure 3. Also the transverse current at position l is zero as is shown in Figure 2. At position 2, Figure 4, the electron has acquired some spiral motion and its displacement from the median plane is shown by the vector r2 in Figure 3. Since wo w the electron lags behind E by the phase angle p2 when it reaches position 2. The transverse electron current in magnitude and phase relative to E is shown by thevector i2 in Figure 2. When the electron has reached position 3 its displacement is given by in and the transverse current by is. It is evident that at position 3 the magnitude of the current is is greater than at position 2 as also is the lagging phase angle. At position 5, the electron has acquired its maximum displacement and the current is due to it is e0 out of phase with E and is purely reactive. From this point on the electron is retarded and the current produced by it has a negative resistive component i. e., a component opposite to E. When electrons enter the condenser plates at all times as in a continuous beam there will be electrons at all positions from 1 to 9 simultaneously and the total effective current will be the vector sum of the currents at each position. This vector sum is shown by I in Figure 2. Thus the total effective current lags behind the field E by Thus E and I are related in phase exactly the same as the potential difference across an inductance and the current through it. If the condenser plates as shown were in parallel with an inductance to form a resonant circuit with resonant frequency w, the passage of the beam of electrons through the condenser plates would increase the resonant frequency.

On the other hand if wn w then the currents i2, s, etc. would lead E and uo-w could be so chosen that the total current would lead E by 90 giving rise to a decrease in the resonant frequency of the parallel circuit.

In effect what the above means is that when the electrons lag the alternating electric field, there is in effect an inductive reactance placed in parallel with the inductive reactance connected across the plates and the equivalent circuit is shown in Figure 5. Inasmuch as this causes a reduction in the inductive reactance of the given frequency, the inductive and capactive reactances do not provide resonance at this frequency. The frequency of the driving voltage must be raised to bring about resonance again. This causes the capacitive reactance to decrease and the inductive reactance to increase so that resonance is established at the higher frequency. Likewise when the electrons are ahead of the electric field the resultant effect is to place a capacitance in parallel with the capacitance of the plates the equivalent circuit being shown in Fig. 6. This reduces the capacitive reactance of the resonant circuit and in order to establish resonant conditions the frequency must be lowered so that the inductive reactance decreases and the capacitive reactance increases. Thus there is provided the means for varying the resonant frequency of the system above and below that which the system would have with no electron beam present. This is the action which takes place in a cavity resonator which is the equivalent of the resonant circuit discussed.

The effect of changing the transit time of the electron through the plates can be seen from the following. Shortening the transit time for a given itu-wo would have the same eect as that produced by shortening the plates. Thus if the plates were terminated at position 7 in Figure 4, the effective current between the plates would be given by the dotted vector in Figure 2. In this case the inductive component of current has been decreased and a resistive component of current is present. Hence changes in the transit time can also be used to change the frequency of a resonant system composed of the condenser plates and a parallel inductance. On the other hand, varying the current density varies the length of the resulant vector I along the X axis since each of the cornponents iz to s is varied. Thus the inductive reactance is in effect varied and hence the frequency.

In Figure 7 is shown the relationship of the change nw in frequency to the k ratio,

which is equal to In this formula a is the natural frequency of oscillation of the rectangular cavity resonator of Fig. l in the fundamental mode with no beam. Figure 7 gives an idea of the behavior and order of magnitude of the change in frequency Aw per milliampere of beam current shown as a function of k for a 4000 megacycle rectangular resonator Y=Z=5.3 cm. and X=.2 cm., when the electrons in the beam enter the resonator after having been accelerated through volts.

From the curve it will be seen that the frequency-shift Aw can be positive or negative depending upon whether k is less than or greater than one. Physically, as described above, this is due to the fact when k is less than one the rotating electrons tend to fall behind the electric eld, thus producing the effect of a lagging current, that is inductance. On the other hand, when k is greater than one, elecsageeags'zs introns .get-ahead ofthe :electricieldfcausinglaJeapacitance teiect andithefrequency zdecreases.

The effectiveness of a giver; current in changing :thefrequency, .that is, irrv producing reactance, is greatest .when zthei magnetic Viield is. adjusted to voptimum .conditions for .the the transit time used. Using the :relationship (1-'k)u-4, givenabove the two valuesfofthe ratio k for maximum frequency .shift Aw for Ytherectangnlar cavity .'resonator XYZ described,"having'adimension Z=5..3 om.,

.a-resonant'frequency yof 4000tmegacycles andra 100 volt :beam,. are approximately 98 and 1.02,tforpositive and Anegative frequency shifts,"respectively. These valuesiof k correspond to the maximum and minimum points on the ,curve shown in Fig. 7. `ThusFigure 7 shows that, for the `resonator described, a value of magnetic eld such that the ratiok is substantially different` from .98 andLOZ causes `the.'etfectfin..the change of' frequency tobe hardly noticefable.

Thus'ameans is providedi forrnarkedly changing `the :resonant frequency of'fthe cavityresonatorby electrons whenthe'magnetic dield issuitably adjusted. The fre- .quency canv be varied as anarbitrary function ofthe .time .by varying the beamcurrentor transit angle,;orboth,. apl:.propriately with the time.

As pointed out' above, changingeither the'electron cur rentdensity or the electron `transit timewill producea corresponding Achange inthe resonant frequencys'of the fresonator'11. With no beam, i. e., zero current density, lthere will be no change in frequency. Asthe` current density is increased' the frequency will be shifted'lmore .and more, in a direction determined solely by the sign of the quantity w-wo. As explained above, when wo is 'less than w, i.-e., w-wo is positive, thefrequencyisl increased, and vice-versa. if a 1lixed voltage is applied.- to

lthe resonator`11 and an alternating voltage applied to thegridlS'by means of the input 20, the current'density '-is varied and hence the-resonant frequency of resonator v`11 is varied. lf ythe-voltage-applicd to the gridf15 is fixed arid the accelerating voltage applied to the resonator variedby'means of the input 2S, the ytransit Ytime of the 40 electrons through the resonator is varied, thusfagain varying 'the resonant frequency of the resonator-11. ltmay l' also be "desirable to utilize'the electrode 1'6 merely asa reflector, sending the electrons back to'the resonator tto` be collected in the resonator. "In thiscase 'the"alterfnating variable voltage may be applied tothe reflector yL16 by'means of the input circuit V25. YIt is, ofcourse, understood in all these cases that magnetron`26 actsas "the driver for the resonator to induce the alternatingfelecltric eld in the proper mode for bringing about the action desired, the change in resonant frequency of the resonator 411 being reected back into the resonators of the magnetron 26 to vary its frequency. Thus an electronic means is provided forfrequency modulating asmagnetron utilizing cavity resonators.

"Thus, 'the tube shown in lFigure l, composedof an appropriate resonator .and beam supplying means and means `for.controlling the beam current'or thetransit time, constitutes a'variable'reactance tubewhich when closely coupled to a high frequency system canlbe vused to vary the resonantfrequency of the systemby introducing Aan almost pure 'inductive or 'capacitive reactance which can be varied with thetime in'any manner.

' The same means of changing frequency can'beincorvporated in a `high frequency generator to obtain agenerator which. can be internally frequency modulated. flt is especially advantageous to apply the'means explained 'above to frequency modulate a magnetron becausear- 'rangementscan be made to Vuse the same magnetic'eld '.usedv for themagnetron. Such a magnetron incorporat- Iing my invention and utilizing amulti-cavity system is shown in Figures 8 to' 12 inclusive.

'In this arrangement an anodeblock Si! is` provided with'acentral opening 31 extending therethrough. A /plurality of anodesegments in the'form-of radially directed anode vanes 32 surround a central space. in which :is axially'mounted an indirectly heated cathode' 33. :It is lobvious that, instead of theflat vanetype anode. arrangement, the block could be provided with radial Aslotsfor obtaining anode segments, or otherV forms or" spaces bev 'tween anode .segments could be provided. 'The slots or ispaces-provide the cavity resonators .32which in the form shownA are provided `between adjacent fanodevanes by. the vanes andthe wall ,of the. openin g.31V through. Vthe Vanode block. ,-'Thesevarious-ianodeYvanesaretstrappedto 85 "45 applied to the controlgrid 66".

uthrough more than two resonators.

vo my invention` of-which l '70 be made in the particularvstructure gether byzmeansofzconducting ring members. 70 and `71,

the rings being connected to alternate vanes, as shown in V1?igs;f9and;10,.toi-facilitateoperation.in the desired mode. iThe cathode33 is` supported by'means of the magnetic 5 finsert 34. Magnetic inserts :34,and 35.are carried'by `bridge members 36'and 37 mounted on the anode block in insulating relationship toA the.v block by means of bolts 3S.;an`d nuts 39,. insulating sleeves '40 and '40', 41

.and 41Jand62 and 62". 'One ofthe .cathode heater 10 .leads-42 is connected' to thel insert34v in electrical contact with the cathodesleeve 33 and the other lead'43 extends through an eyelet and is sealed Vthrough the header 45 of the envelope by `means of the glasslead and seal -'43.

The bridge member 36 is electrically connected to the l5 lead 44 which extends through and is sealed in the header -45 ofthe envelopeSS by means of the insulating tube-44'.

The anode block 30 maybe supported from the header '45 bymeans 4of the-supports-46 and47. An output coupling-loop 'e0 Ydisposed in one of the cavity resonators terminatesl in a coaxial line 51-52 is sealed at its end by Vmeans of the cap53. A ypermanent magnet having poles W56 and 56', provides 'the usual magnetic field in the Vcathode space and in the resonators, in a direction parallel to the cathode 33.

0lnaccordance with my invention I provide one or more indirectly heated cathode sleeves 60 supported' by the'- insert '3SE by vmeans of Athe insulating collars' 61, the leads "'52 and 63 for the cathode and for the cathode heater extending through and sealed byitubular'members r64. Insulatingly` mounted on theend of each cathode sleeve 60 Iby'meanstof' the insulating collar 66 and supporting ring l66" is gridV having iead'o sealed through the insulating "member Each 'beam B of electrons from a cathode is directed through one of the cavity resonators 35 towards the collector 67 also :provided with a lead.68

sealed'thro'ugh the linsulating tubular member.

`T he operation of the internally-modulated magnetron `of Figsr8-l2iis similark to that ofFig. l, the principal .diference being that the cavity'resonators of the .mag- "netron1inFigs-sS-l2 are excited by the space charge'revolving in the anode-cathode space whereas the cavity 'resonator of.Fig..l is excited by an external oscillator closely coupled thereto.

To frequency' modulate the magnetrona signal maybe As an alternative, how- -:ever, the gridmay. beeliminated and the velocity of the electrons controlled byapplyinga radio frequency voltage: between. the anode block 30. and'cathode 60. Elec- ^trode"67-may be used as a reectorin--Which case elec- .ioz'trons are repelled back through the resonator and .col-

4lected by the anode' vanes,'thus varying the transit time -vof the electrons through the resonator. It is obvious thatone or more modulating cathodes could be utilized and that the modulating beams B could be projected The electron .gun gunY and a single the arrangement could. also be. replaced by an annular collector. 'These are all equivalents of shown.

"The form of'the invention disclosed inF-iguresS G0 'through .'12 is claimed in applicants co-pending applica- 'tion,"`Serial"No. 23,045, led April24, 1948, whichisa continuation-in-part of my copending application ,Serial No.' 563,732, referredto above.

Whilell have indicated the4 preferred embodimeutsof 4 am now aware and havealso indicatedlonly two specitic ,applications for whichmy inventionmay be employed, it willbeapparent that my 'invention is by no meanslimitedto Athe exact forms illustratedtorthe use indicated, but` that many variations may usedand the purpose for which 1t 1s employed without .departing from the .scope of my inventionas setforth in the appended claims.

WhatI Vclaim isz l. A variable frequency4 device including hollow reso- 5.,nant means-normally resonant at a predetermined frequency, cathode means adjacent -sai'd hollow resonant `means forfdirecting a beam of electrons along a path withinsaid hollow resonant means. means Yadjacent said hollow resonant means for providing a constant magnetic .-eldwithin said hollow resonant means'extending along .Eandparallel to -said'path, means coupled'to said vhollow resonant meansforenergizing said hollow resonant means to establish. an alternating electric eld therein normalto said-.path, and .means adjacent said cathode.rneansfor varying` thefow of l saidelectron' beam wherebyV the reso- 7 nant frequency of said hollow resonant means can be varied.

2. A variable frequency device including a cavity resonator having an opening in the wall thereof, cathode means adjacent and exterior to said cavity resonator for directing a beam of electrons along a path through said opening and into the interior of said resonator, means adjacent said resonator for providing a constant magnetic field within said resonator extending along and parallel to said path, means coupled to said cavity resonator for exciting said resonator to provide an alternating electric field therein normal to said path during operation of said device, and means adjacent said cathode means for varying said electron beam for varying the resonant frequency of said device.

3. A variable frequency reactance device including a cavity resonator having an opening in the wall thereof and a pair of opposed surfaces, cathode means adjacent and exterior to said cavity resonator for directing a beam of electrons along a path extending through said opening and into the interior of said resonator and intermediate said opposed surfaces, means coupled to said cavity resonator for establishing an alternating electric field therein extending between said opposed surfaces, means adjacent said resonator for providing a constant magnetic field within said resonator extending along and parallel to said path, and means adjacent said cathode means for varying the electron beam for varying the reactance and resonant frequency of said device.

4. A resonant device including a cavity resonator of rectangular form and having a pair of oppositelydisposed apertures in the walls thereof lying along an axis of said resonator, and means for changing the resonant frequency of said resonator comprising cathode means adjacent said cavity resonator for directing a beam of electrons along said axis through said apertures, means adjacent said cavity resonator for providing a constant magnetic field within said resonator and extending along said axis, and means coupled to said cavity resonator for exciting said resonator to provide an alternating electric field within said resonator normal to said axis.

5. A variable frequency device according to claim 4, further including means in the path of the beam for varying the electron beam for varying the resonant frequency of said resonator.

6. An electron discharge device comprising a cavity resonator having a normal resonant frequency and including a pair of substantially parallel flat opposed surfaces, means coupled to said resonator for providing an alternating electric field extending between said surfaces within said resonator, means adjacent said resonator for providing a constant magnetic field within said resonator intermediate and extending parallelto said opposed surfaces, and means including a cathode adjacent said resonator for directing a beam of electrons within said resonator along a path parallel to said magnetic field and normal to said electric field during operation of said device for changing the resonant frequency of said device.

7. An electron discharge device comprising a cavity resonator having a normal resonant frequency, means adjacent said resonator for projecting a beam of electrons along a predetermined beam path within said resonator, means adjacent said resonator for establishing a constant magnetic field substantially axially of said beam path within said resonator, means coupled to said resonator for establishing an alternating electric field of said normal resonant frequency Within said resonator and transverse to said path whereby during operation of said device the electrons of said beam traverse spiral paths around said beam path within said resonator, and means in the path of said beam for varying said beam to vary the resonant frequency of said resonator.

8. An electron discharge device comprising a cavity resonator having inductance and capacitance determining a normal resonant frequency and including a pair of opposed surfaces, means adjacent said resonator for projecting a beam of electrons within said resonator along a predetermined beam path in the space between said opposed surfaces, means adjacent said resonator for establishing a constant magnetic field substantially axially of said beam path and within said space, means coupled to said resonator for establishing an alternating electric field of said normal resonant frequency extending between said opposed surfaces and transverse to said beam path, whereby during operation of said device the electrons of,

said beam traverse spiral paths around said beam path Within said space and means in the path of said beam for varying said beam to vary the resonant frequency of said resonator.

9. An electron discharge device comprising a cavity resonator having inductance and capacitance determining a normal resonant frequency and including a pair of opposed surfaces, means including a cathode and a collector positioned adjacent and on opposite sides of said resonator for projecting a beam of electrons along a predetermined beam path within said resonator in the space between said opposed surfaces, means adjacent said resonator for establishing a constant magnetic field substantially axially of said beam path and within said space, and means coupled to said resonator for establishing an alternating electric field of said normal resonant frequency extending between said opposed surfaces and transverse to said path, whereby during operation of said device the electrons of said beam traverse spiral paths around said beam path within said space, and means including a control grid adjacent said cathode for modulating the charge density of said beam to modulate the resonant frequency of said resonator.

l0. An electron discharge device comprising a cavity resonator in the form of a rectangular box having inductance and capacitance determining a normal resonant frequency and including a pair of opposed parallel walls,

means including a cathode and a collector positioned adjacent and on opposed sides of said resonator for projecting a beam of electrons within said resonator along a beam path substantially parallel with said opposed walls, means adjacent said resonator for establishing a constant magnetic field substantially axially of said beam path and within said space, means including a coupling loop coupled to the interior of said resonator for establishing an alternating electric field of said normal resonant frequency extending between said opposed walls and transverse to said path, whereby during operation of said device the electrons of said beam traverse spiral paths around said beam path within said space, and means including a control grid adjacent said cathode for modulating the charge density of said beam to modulate the resonant frequency of said resonator.

1l. An electrical system comprising a cavity resonator having a normal resonant frequency, means for projecting a beam of electrons along a predetermined beam path within said resonator, means for establishing a constant magnetic field substantially axially of said beam path and within said resonator, and means for establishing an alternating electric field of said normal resonant frequency within said resonator and extending transverse to said path, whereby the electrons of said beam traverse spiral paths around said beam path within said resonator out of phase with said alternating electric field therein and thus produce a substantial reactive effect upon said resonator to change its resonant frequency.

l2. An electrical system according to claim 1l, further including means for varying said beam to vary the resonant frequency of said system.

13. An electrical system comprising a cavity resonator having a normal resonant frequency, means for projecting a beam of electrons along a predetermined beam path extending through said resonator, means for establishing a constant magnetic field substantially axially of said path and through said resonator, and means for establishing an alternating electric field of said normal frequency within said resonator and extending transverse to said path, the intensity H of said constant magnetic field, the transit time Ir of said electrons through said resonator and the normal resonant frequency f conforming to the relation v-(Zirf-He/nll, where 1r is 3.1416, and e and m are the charge and mass, respectively, of an electron, whereby the electrons of said beam traverse spiral paths around said beam path through said resonator out of phase with said alternating electric field and thus produce a maximum reactive eect for a given transit time for a given beam current upon said resonator to change its reactance and hence its resonant frequency.

14. An electrical system according to claim 13, further including means for modulating the charge density of said beam for modulating the resonant frequency of said system.

l5. A method of changing the reactance and resonant frequency of a cavity resonator without loading the latter, comprising the steps of directing a beam of electrons through said resonator, simultaneously subjecting at least a portion of said beam within said resonator to a transverse alternating electric field and a substantially axial constant magnetic field and adjustingihe transit time of, said-..electronssthrough said electric field. to a.,val1ie;at

which the net transfer of 'energy between said electric field andeach electron is zero.

16. A-method in accordance. with' claim 15, further including the step of'varying. the iiow of saidb'eamof electrons.

17'. Amethodof changing the reactance andresonant frequency of ia cavity resonator havinga normal vresonant angularfrequency, comprising the steps-of directing a beam of electrons along a" beam path within said resona- 'tor simultaneously subjecting at least 'ai portion of` said beam to a transverse alternatingv electric fieldfof said resonant frequency and a substantially f axial] constant magnetic field, and'adjusting the intensity of said magnetic field to make H e/ m slightly different-.from saidresonant angular frequency, where H is the magnetic'` field intensityiand e and m are theelectric charge and lmass, respectively, of an electron.

18'. A-methodV in accordance with claim 17, further the magnetic field intensity H is adjusted relative to theY transittime ,v-of the electrons through. said resonator and the normal angular resonantfrequency w to make approximately equal to 4.

20. An electrical device comprising a cavity resonator normally resonant at a predetermined frequency and having a pair of opposed surfaces, and means for changing the resonant frequency of said resonator comprising means for projecting a beam of electrons along a predetermined initial beam path intermediate said surfaces and means for causing the electrons of said beam to traverse spiral paths around said beam path and intermediate said surfaces, said last named means comprising means coupled to said resonator for establishing an alternating electric field extending between said surfaces and transverse to said path, and means adjacent said resonator for providing a constant magnetic field in the space between said surfaces and substantially parallel to said beam path.

2l. An electrical device according to claim 20, further including means in the path of the beam for varying said beam to vary the resonant frequency of said resonator.

22. An electrical system comprising a cavity resonator having a normal resonant frequency, means for projecting a beam of electrons along a predetermined initial beam path within said resonator, means for establishing a constant magnetic field substantially parallel to said beam path and within said resonator, and means for establishing an alternating electric field of said normal resonant frequency`within said resonator and extending transverse to said path, the transit time of the electrons within said resonator being adjusted to a value at which the net transfer of energy between said electric field and each electron is zero, whereby the electrons of said beam traverse spiral paths around said beam path within said resonator out of phase with said electric field therein, producing a substantial reactive effect upon the resonator to change its resonant frequency, without loading the resonator.

23. In combination, a cavity resonator having a pair of opposed surfaces, and means for varying the impedance of said cavity resonator comprising means for establishing an alternating electric field extending between said surfaces within said resonator, means for projecting a beam of electrons within said resonator along an initial beam path intermediate said surfaces and transverse to said electric field, means for establishing a constant magnetic field in the space between said surfaces and substantially parallel to said beam path to cause said electrons to traverse spiral paths around said beam path and between said surfaces, and means for varying the flow of said electrons.

24. In combination, a cavity resonator having a pair of opposed surfaces and a normal resonant frequency, and means for variably loading said cavity resonator without affecting its resonant frequency comprising means for establishing an alternating electric field extending between said surfaces within said resonator, means for projecting substantiallyequal to.21rj", where e andm are the charge'.

andl mass,- respectively, of an'electron, nis 3.1416, and f issaid`normal resonant frequency of.'V said resonator,

wherebythe electronstraverse spiral paths'aroundsaid beam path: andbetween .said surfaces in phase with said electric fieldat all times, and means for Varying the fiow of. saidfelectrons.

25. An electrical devicein accordance with claim 2t), comprising a reflector electrode disposedV in vsaid .beam path on the opposite side of said resonator from said beam projecting '.means.

26. An eiectricalfdevice inaccordance` with claim 25, comprising means for applying a variable voltage to said refiector electrode.

27. Thefcombination,recitedin. claim23, wherein said last-named Vmeanscomprises .means for. .varying the charge density of said beam.

2S. The combination recited in claim 23, wherein said last-named means comprises means for applying a variable accelerating voltage to said resonator.

29. The combination recited in claim 23, wherein said last-named means comprises a refiector electrode disposed on the opposite side of said resonator from said beam projecting means, and means for applying a variable voltage to said reflector electrode.

30. In a high frequency generator system including a generator, means for providing a constant magnetic field, and an electronic device coupled to said generator and comprising means for projecting an electron beam along an initial path parallel to said magnetic field; the method of variably loading said generator without changing the frequency thereof, comprising the steps of adjusting the intensity of said magnetic field to provide substantially optimum loading of and negligible reactive effect upon said generator, and varying said loading in response to control signals.

31. The method of variably loading a high frequency generator, including the steps of coupling said generator to a cavity resonator, providing a constant magnetic field through said resonator, projecting a loading electron beam through said cavity resonator and along an initial path substantially parallel to said magnetic eld, adjusting the intensity of said magnetic field as a function of the operating frequency of said generator to provide maximum loading and negligible reactive effect by said electron beam, and varying the energy-absorbing ability of said beam to vary the loading of said generator.

32. A high frequency system including a generator adaped to provide high frequency oscillations, a variableconductance electron beam device coupled to said generator, said device comprising means for projecting a beam of electrons along an initial beam path, means for providing a constant magnetic field parallel to said beam path, the electron rotation frequency of said magnetic field being substantially equal to the angular frequency of said oscillations, and means for varying the conductance of said beam to vary the loading of said generator with negligible frequency modulation thereof.

33. A high frequency system including a cavity resonator, means coupled to said resonator for exciting oscillations therein, means for projecting an electron beam along an initial beam path extending through said resonator, means for providing a constant magnetic field parallel to said beam path, the electron rotation frequency of said magnetic field being substantially equal to the angular frequency of said oscillations whereby said beam loads said resonator with negligible reactive effect thereon, and means for varying the conductance of said beam to vary the loading of said resonator.

34. A magnetron pilot cavity resonator, said resonator having a capacitive gap formed by surfaces therein across which high frequency electric fields are impressed, electron means for varying the effective capacity of said gap, said means including a cathode, an anode, and a grid adjacent said capacitive gap and adapted to pass an electron beam therethrough substantially parallel to said 1 1 surfaces whereby the control of the density of said electron beam may be utilized to vary the resonant frequency of said resonator, and means for generating a magnetic ield substantially parallel to and including said electron earn.

35. A magnetron pilot cavity resonator, said resonator having a capacitive gap formed by surfaces therein across which a high frequency electric field is impressed, electron means adjacent said capacitive gap for varying the elective capacity of said gap, said electron means including a cathode, an anode, and a control grid, said electron means adapted to pass a beam of electrons through said gap at right angles to said electric ield whereby the electron density of said electron beam within said gap may be varied, and a pair of magnet poles for producing a magnetic eld parallel to the axis of and including said electron beam whereby said electron beam is stabilized and concentrated in said gap.

References Cited in the file of this patent UNITED STATES PATENTS Number Cil Number yNumber 12 y Name Date Lindenblad Feb. 28, Fritz Jan. 16, Hollmann Apr. 30, Webster et al Dec. 31, Blewett et a1 May 13, Brett et al. June 3, Varian June 17, Fraenckel Dec. 16, Brown Apr. 14, Hansen et al. Feb. 23, Llewellyn Mar. 2, Nergaard Sept. 21, Percival Oct. 12, Fremlin I an. 4, Linder June 11, Anderson et al. Aug. 6, Hansen et al. Aug. 27, Bowen Feb. 25, Goldstine June 29, Smith Oct. 31,

FOREIGN PATENTS Country Date Australia Oct. 22, 

